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Figures

Fig. 1: Hypothetical probability density distributions of measured plasma brain natriuretic peptide (BNP) levels in 2 subgroups of a study population. The cutoff point for a diagnosis of congestive heart failure (CHF) is 100 pg/mL. Patients with a negative test result for CHF (left-hand curve) are younger, with known asthma and no risk factors for CHF. The patients with confirmed CHF are older, and the disease is clinically severe and unequivocal. Clinicians in the emergency department have little uncertainty regarding the cause of dyspnea in any of these patients.

Fig. 2: These hypothetical probability density distributions reflect a study population of middle-aged patients who all have recurrent asthma and chronic CHF. The patients whose dyspnea is caused by asthma exacerbations look clinically similar to those whose symptoms are caused by acute CHF.

Fig. 3: Likelihood ratios (LRs) and spectrum of disease. The likelihood ratio of a test result represented by a point on the horizontal line is the height of the right-hand bell curve (patients with the disease of interest) divided by the height of the left-hand bell curve (patients without the disease of interest) at that point.